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2009年2月13日 (金)

人工衛星衝突 宇宙ごみ対策を強化せねば

The Yomiuri Shimbun (Feb. 13, 2009)

Space debris measures must be strengthened

人工衛星衝突 宇宙ごみ対策を強化せねば(213日付・読売社説)

Our planet is surrounded by space debris, a matter that is becoming of increasing concern.


The collision of a U.S. satellite weighing about half a ton with a Russian satellite about twice that size, about 800 kilometers above the Earth's surface, reportedly produced a huge amount of debris. We wonder if the collision could have been avoided if their orbits had been adjusted.


Since the world's first satellite was launched in 1957, thousands of satellite launches have taken place, meaning there are a large number of objects drifting around the Earth.


Among the space debris in orbit around our planet are satellites that are no longer functioning, either because they have outlived their usefulness or have malfunctioned. Space debris also includes rocket booster parts, the remains of collisions among space vehicles and equipment dropped by astronauts. It is estimated that there are between 30 million and 40 million items of space debris currently adrift, weighing a total of about several thousand tons.


In 2007, China's destruction of one of its weather satellites produced a huge amount of debris.


If nothing is done to address the problem, mankind faces serious problems in its use of space as space debris has massive destructive potential.


Such debris can travel at speeds of about 5 kilometers per second, while the energy generated from a collision of debris even just 1 centimeter across can be equivalent to that of a car crash on a highway. The smashing of satellites into one another is clearly disastrous.



An international problem

Previously, a French satellite was seriously damaged after colliding with space debris. In the United States, a rocket launch was postponed to prevent a collision with space debris.


What is of particular concern this time is the threat to the International Space Station, which has been under construction with the participation of Japan and other nations. The ISS orbits about 400 kilometers beneath where the latest collision took place, and it is unlikely that debris will hit the ISS. But it is still possible that debris could pass over the ISS.


An extended stay at the ISS by Koichi Wakata, the first of its kind for a Japanese astronaut, is expected to begin soon, and it is of some concern that the space shuttle flying to the ISS could be affected by the debris.


The ISS is equipped with protective walls designed to absorb shocks from small debris and the station would alter its orbit to avoid large pieces of debris, which are tracked by radar from the ground by the U.S. military when a shuttle is to be launched.



Breaking the cycle

But if the amount of debris continues to increase, it will become more difficult to take all possible preventive measures. Greater precautions must therefore be taken to try and prevent troubles that could affect the ISS.


A further concern is the apparent vicious circle of increased space debris from collisions, which in turn creates more potential for destruction, as can be seen in the latest collision. The growing amount of debris means the probability of more collisions is set to explode in about a decade or so.


International guidelines state that large satellites should be brought back to Earth. But is this enough? Is there no way that space debris can be collected? Japan needs to call on other nations that have space development programs to address the issue and play a more active role in strengthening measures to tackle the problem.


(From The Yomiuri Shimbun, Feb. 13, 2009)

20092130145  読売新聞)


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